"We eventually asked ourselves, 'What if we're not seeing results in these two separate dishes because in the body, the two aren't separated. What if these two cell types somehow act in concert and need to communicate with one another as they otherwise would in vivo in order for CO to exert its beneficial effects?'"
To address this question, coauthor Beek Yoke Chin, PhD, developed a simulated blood vessel by growing the cells on a semi-permeable membrane, which enabled the two cell types to "communicate" with one another through pores. And that, says Otterbein, was when the scientists observed that in this "co-culture" setting, CO was able to induce death of the smooth muscle cells without adversely affecting the viability of the endothelial cells.
"We discovered that endothelial cells must be present ?and be able to generate NO via nitric oxide synthase [NOS3] -- in order for CO to induce the death of the smooth muscle cells and reverse the symptoms of PAH," explains Otterbein. To further test the role of the nitric oxide, the co-culture was treated with a select inhibitor of NOS3. Under these conditions, he adds, CO was unable to induce death to the same degree as in control-treated co-cultures.
"We concluded that the physical interaction between the two cell types plus the ability to generate NO was crucial for the positive CO effects," he says, adding that studies are now underway to determine the mechanism by which CO exposure leads to the increase in NO generation.
"Our hope is that CO will find a place in the clinic as a therapeutic option for the treatment of disease," concludes Otterbein. "CO has been around since before life began on earth and, in fact, it is thought to have contributed to the origin of life. Perhaps this was a sign of its necessary role in biology."